Consumer products usually have two lifetimes, the best before date if unopened and the usually more restrictive useful life after it has been opened. Although devices are available which integrate the temperature/time environment of e.g. food products to show the point in time at which the contents are unsafe or should not be consumed, no devices are available which provide information of usage lifetime calculated independent of temperature.
For many packaged consumer products, the usable lifetime of the product is considerably reduced when the package is opened. In addition, many products such as cosmetics, creams or sun-creams have a lifetime after which the product effectiveness is substantially reduced. Moreover certain cosmetic products such as mascara and medication actually carry an increased risk of infection once beyond the lifetime stipulated by manufacturers of such products, e.g. 3 months, but this lifetime currently cannot be tracked by the consumer.
In GB 2397022 an air freshener is described which includes an end-of-life indicator. The air freshener includes a lifetime marking on the product covered by an additional gel which shrinks as a result of exposure of the additional gel to air. The shrinkage of the additional gel ultimately results in exposure of the lifetime marking as an indication that the device needs to be replaced. The additional gel shrinks as a result of evaporation and thus is susceptible to variations in ambient temperature.
A timing device for packaging enclosures is described in GB 2344101. The packaging consists of a container with a screw cap and the screw cap includes an indicator disk mounted on the inside of the cap but visible through a window in the screw cap. The indicator disk is constructed from a pair of foil sheets that are bonded together to form two separate sealed compartments. One of the compartments contains humid air and the other a water-sensitive colour changing composition. When the screw cap is first removed from the container, to access the contents of the container, the bonding between the two compartments in the indicator disk is broken. Exposure of the water-sensitive composition to the humid air causes a colour change. The rate at which the colour change occurs is determined by a second composition with which the water-sensitive composition is mixed. A similar timing device is described in WO 01/26993. This describes a sealed compartment containing a colour-changing substance mounted in the cap to a container. Removal of the cap from the container breaks the seal to expose the colour-changing substance to an activation chemical thereby triggering the colour change which is viewed via a transparent section of the container cap.
A different colour-changing device is described in GB 2243825. A multi-laminar thermoplastic tamper-evident member is described in which one of the thermoplastic layers has a warning substance printed or sprayed on it which is reactive to ambient air. The tamper-evident member is intended for application to a container in a manner which results in at least one of the layers of the tamper-evident member being broken when the container is opened. Breakage of at least one layer of the member exposes the warning substance to ambient air which in turn results in the substance changing colour as a warning that the container has been opened.
In GB 2419868 a food date indicator is described which comprises a label for attachment to a package. The label is formed of a sealed envelope within which an oxygen-sensitive strip is located. Opening the package results in the label being torn at one end to expose the inner oxygen-sensitive strip. Oxidation of the strip causes a colour change that over a predetermined period of time extends along the length of the strip. Thus the amount of the strip that has changed colour is representative of the time since the package was first opened.
A timing device is also described in U.S. Pat. No. 7,372,780 in this case comprising two electrodes with an electrochromic material between the two electrodes. The timing device is attached to an activating mechanism that connects the two electrodes forming a closed circuit. Once connected, the circuit results in a colour change in the electrochromic material as a result of depletion or partial depletion of the material.
An alternative timing device which is capable of measuring a time frame between a first opening and closing of a package and a predetermined later time is described in WO2009/129998. This timing device employs a diffusion path integrated into a closure cap.